Steps for obtaining a press-molded article using a band plate as a starting material are performed in the following sequence.
A blank is cut from a band plate by a blanking press or another device. The blank is conveyed near to a molding press machine, loaded into the molding press machine by a robot, and press-molded by the molding press machine.
The molding press machine is provided with a molding die. The blank must be placed properly in the molding die. However, the blank may not always be placed in the desired position. As a countermeasure, a centering device is installed to carry out the positioning of the blank.
A variety of centering devices have been proposed (e.g., see Patent Literature 1).
The centering device disclosed in Patent Literature 1 uses implements to grasp blanks. When the blanks have different shapes, numerous implements must be prepared. Manufacturing the implements then incurs high costs, and space for storing the implements is needed. Scratches may also be left in the blanks. When the implements are moved more quickly to increase the conveying speed, the scratches become more prominent.
Implements are replaced with each different blank shape, but the molding press machine is stopped during this replacement. The rate of operation of the molding press machine decreases.
Furthermore, when an attempt is made to simultaneously convey two blanks, controlling the implements is becomes complicated, and as a result it is difficult to convey the two blanks.
It is possible for the blanks to be transported and correctly positioned by a robot without the use of implements, but in this case, a single robot takes too much time and is too slow for the cycle time. When two robots are used in order to make the process fast enough, interference between the robots becomes a problem, control becomes complicated, and more space is needed to install the robots.
Specifically, the centering device of Patent Literature 1 presents problems in that it is difficult to increase the speed, the rate of operation is low, and the device cannot be adapted to conveying a plurality of workpieces.